9 1/2 year ol girl is having trouble breathing - what could be wrong?

Miranda is 9 1/2 and is in fourth grade. She was dizzy and having trouble breathing right before gym class at school today. She went to the nurse and they gave her two glasses of water and sent her back to class. She still was feeling bad. What could be wrong? What should I do?
Update: This started a couple of days ago, but I thought it was do to the hot weather. Today it was around 58 and raining though. She usually doesn't mind going to gym class, and anyways they were doing one of her favorite activities today. It occurs out of random, I guess it started when they were watching a movie on... show more This started a couple of days ago, but I thought it was do to the hot weather. Today it was around 58 and raining though. She usually doesn't mind going to gym class, and anyways they were doing one of her favorite activities today. It occurs out of random, I guess it started when they were watching a movie on Thomas Eddison in the classroom. She assured me she wasn't scared of anything, for the nurse suspected something like that also.
Update 2: She had eaten just as usual. Nothing more or nothing less. She also isn't allergic to anything much. So, I'm doubting it could be allergies. She's had the croup before, could it be this again? She said she was talking to her friend and she said that she thinks it might be asthma, her friend is pretty... show more She had eaten just as usual. Nothing more or nothing less. She also isn't allergic to anything much. So, I'm doubting it could be allergies. She's had the croup before, could it be this again? She said she was talking to her friend and she said that she thinks it might be asthma, her friend is pretty knowledgeable about diseases, for she has Addison's Disease. Her friend said it could also be something with her adrenal gland, like her disease. Anything of this sound right?
Update 3: She said she was feeling somewhat tired, but I believe she slept a lot last night. She was also pretty dizzy for part of this time. Any of these symptoms for asthma or any other disease like that?
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